Re: intel_pstate divide error with v3.13-rc4-256-gb7000ad

[Josh Boyer]

On Fri, Dec 27, 2013 at 7:47 AM, Gleb Natapov <gleb@xxxxxxxxxx> wrote:
> On Fri, Dec 27, 2013 at 12:24:22PM +0000, One Thousand Gnomes wrote:
>> On Tue, 24 Dec 2013 21:36:01 +0530
>> Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>>
>> > Adding Dirk..
>> >
>> > On 24 December 2013 20:06, Josh Boyer <jwboyer@xxxxxxxxxxxxxxxxx> wrote:
>> > > Hi All,
>> > >
>> > > We've had a report [1] that the pstate driver causes KVM guests to
>> > > fail to boot because of a divide error.  See the backtrace below.
>> > >
>> > >     4.839784] Intel P-state driver initializing.
>> > > [    4.859972] Intel pstate controlling: cpu 0
>> > > [    4.867653] cpufreq: __cpufreq_add_dev: ->get() failed
>> >
>> > After a call to ->init(), ->get() is supposed to work.
>> > @Dirk: Any idea why it failed?
>> >
>> > And then I don't know what made this divide by zero to happen :)
>>
>> > > [    4.878127] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
>>
>> Emulator bug perhaps ?
>>
> KVM does not emulate P-states at all. intel_pstate_init() calls
> intel_pstate_msrs_not_valid() before printing "Intel P-state driver
> initializing."  which suppose to fail since it checks that two reads of
> MSR_IA32_APERF return different values, but KVM does not emulate this msr
> at all, so both calls should return zero (KVM suppose to inject #GP, all rdmsrl
> are patched to be rdmsrl_safe in a guest).
>
> Anything interesting in host dmesg? Is it reproducible?

Seems reproducible.  I forgot to link to the actual bug in my original
report, but you can find it here:

https://bugzilla.redhat.com/show_bug.cgi?id=1046317

Adding Richard and Kashyap on CC.

josh
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